An oil seal ring for sealing hydraulic oil is mounted on necessary positions of equipment such as the AT and the CVT. For example, the oil seal ring is mounted on a pair of annular grooves formed on a rotary shaft inserted into a shaft hole of a housing by spacing the annular grooves at a certain interval so that a side surface and an inner circumferential surface of each oil seal ring receive the hydraulic oil supplied from an oil passage disposed between both annular grooves. An opposed side surface and an outer circumferential surface of each oil seal ring seal a side wall of the corresponding annular groove and the inner circumferential surface of the housing. A sealing surface of each seal ring slidably contact the side wall of the corresponding annular groove and the inner circumferential surface of the housing, with the sealing surfaces of both seal rings holding the hydraulic pressure of the hydraulic oil between both seal rings. The above-described oil seal is demanded to have a small frictional loss and a sufficiently high oil sealing performance. In recent years, to improve fuel consumption is an important problem to be solved. To this end, the seal ring is desired to maintain a satisfactory sealing performance and at the same time have improved low torque generation performance.
As such a seal ring, as shown in FIG. 9, the seal ring is proposed as disclosed in a patent document 1. FIG. 9 is partly cutaway view of the seal ring. As shown in FIG. 9, in the seal ring, a fluid flow path for introducing a fluid to be sealed thereinto is formed on the sliding contact surface 21 of the seal ring, and the projected portion 23 (the concave portion 22 is formed at both sides of the projected portion) is formed in the middle of the flow path to generate a dynamic pressure so that the surface pressure is decreased.
As shown in FIG. 10, another seal ring is proposed as disclosed in a patent document 2. FIG. 10 shows a state in which the seal ring is mounted on the annular groove. As shown in FIG. 10, the seal ring is mounted on the annular groove 31, and the concave portions 34 having the construction in which the edge of the end portion of the non-contact portion 33 is partly cut out are formed on the end portion of the non-contact portion 33 of the sliding contact surface 32.